Mt. Kiro, on the island of Oshima in Ehime Prefecture, has long been famous for its stunning 360-degree views of the Seto Inland Sea. Visible from the top of Mt. Kiro are Kurushima Strait and the Geiyo Islands to the west and north, with the Hiuchinada Sea to the east, and Imabari Port and Imabari City to the south. But the Kirosan Observatory, designed by architect Kuma Kengo and opened in 1994, is as much about the view from the bottom as from the top.

Kuma, who is also the architect behind the New National Stadium for the Tokyo 2020 Olympics, wanted to avoid building a structure that would stand out when people looked at Mt. Kiro. There was just one problem: the top of Mt. Kiro had already been leveled off to create the existing observation park. Kuma decided to try restoring the mountain’s original peak and then building the Kirosan Observatory inside it. The result is an impressive piece of invisible architecture.

Visitors to Kirosan Observatory walk up a long staircase through a slit cut into the top of the mountain. Inside is a structure like an open-topped concrete bunker, with stairs and walkways leading off in different directions. Walking upstairs leads to the top of Mt. Kiro, where visitors can then follow a route designed to mimic the shape of a single pen stroke. Unlike most viewing platforms, there is no single ideal vantage point for all the tourists to queue up for selfies. Each and every part of the route shows a different view of the Seto Inland Sea.

龟老山位于爱媛县大岛，长久以来以其壮观的濑户内海360度美景而闻名遐迩。从龟老山山顶可以欣赏夕阳徐徐沉入碧海的壮丽景观，还有世界首座三联悬索桥——“来岛海峡大桥”以及日本三大急潮之一——“来岛海峡”大潮，天气晴朗时，甚至可以望至西日本最高峰“石锤山”。建筑师隈研吾（1954-　）设计的龟老山展望台自1994年开放以来，从山麓仰望龟老山的景致毫不逊色于山顶视野，美不胜收，动人心魄。

负责设计2020年东京奥运会新国立竞技场的建筑师隈研吾，希望赋予龟老山一个纯净无碍的仰视视野，而要实现这一构想，则需修复此前为建造公园而削平的山顶。隈研吾还原山顶后，在其内部建造了龟老山展望台，一座巧妙的隐形建筑就此诞生。

一条长长的台阶路自山顶直通展望台，内部是混凝土结构配合开放敞顶，台阶和通道则向四面八方延伸。沿着如同一笔连成的路线，登上台阶就此抵达龟老山山顶，从各个角度随意望去，濑户内海的万千景象绝无死角，任您游目骋观，皆是美景。因此，也就无需像一般展望台那样指定一处位置供游客排队自拍。